1. Field of the Invention
The present invention relates to a driver device for a recording head, particularly to a driver device suitable for use in a recording head of an ink jet printer which is capable of ejecting an ink.
2. Discussion of Related Art
A color ink jet printer typically comprises an ink jet head where four nozzle rows for respective colors (for instance, yellow (Y), magenta (M), cyan (C), and black (Bk)) are formed. A piezoelectric element is disposed correspondingly to each of the nozzles, to apply a pressure to an ink of the respective color, to eject the ink from the nozzle. Each of the piezoelectric elements of the ink jet head is driven by an electric potential applied from a driver IC which is mounted on a carriage together with the ink jet head. The driver IC on the carriage and a main body of the ink jet printer are connected to each other via a signal cable such as a flexible wiring board.
Recently, an arrangement where plural kinds of waveform signals are supplied is employed, so that a printing with intensity gradation is enabled. There is also employed an arrangement where plural kinds of waveform signals are supplied so that a waveform of a signal used for ejection of an ink can be changed depending upon whether the ink has been or will be ejected at the immediately previous or subsequent ejecting timing, in order to reduce an influence of a residual vibration after an ink ejection, which arrangement may be called a historical control. In JP-A-2000-158643, there is disclosed an arrangement where such plural kinds of waveform signals are selectively applied to each of the piezoelectric elements.
A conventional driver IC for driving the piezoelectric elements will be described by referring to a diagram of FIG. 16 and a timing chart of FIG. 17.
As shown in FIG. 16, the driver IC 160 includes a shift register 162 as a serial-parallel converter, which converts print data serially transmitted from an external device, into parallel data for each nozzle. A delay flip-flop 164 latches the parallel data. A multiplexer 166 selects one of plural kinds of waveform signals which is designated by the print data for each nozzle, and outputs the selected waveform signal to a drive buffer 168 At last, the drive buffer 168 supplies the waveform signal, as a drive signal with a predetermined voltage, to a piezoelectric element corresponding to the nozzle.
There will be provided further detailed description of each element of the driver IC 160.
Into the shift register 162 is inputted print data of three bits SIN0, SIN1, SIN2 each serially transmitted in synchronization with a transmission clock signal CLK, from a circuit board in the main body of the printer. A bit length of the shift register 162 corresponds to a product of the number (e.g., 75) of nozzles in each nozzle row and the number of bits of the print data. As shown in FIG. 17, the shift register 162 converts the print data SIN0, SIN1, SIN2 into parallel data in accordance with rising edges of the transmission clock signal CLK, and outputs parallel print signal Sn-0, Sn-1, Sn-2 for each of the 75 nozzles, where “n” represents one of numbers 0-74. In the following description, too, n represents one of numbers 0-74.
The D flip-flop 164 outputs print signal Sn-0, Sn-1, Sn-2 as a selecting signal SELn-0, SELn-1, SELn-2, in accordance with rising edges of a strobe signal STB transmitted from the circuit board in the main body of the printer, as shown in FIG. 17. A bit length of the D flip-flop 164 is the same as that of the shift register 162.
The driver IC 160 receives waveform signals FIRE1, FIRE2, FIRE3, FIRE4, FIRE5, FIRE6 outputted from a waveform signal generating portion (not shown) in the circuit board in the main body, through respective signal lines. The waveform signals FIRE1-6 are inputted into the multiplexer 166.
The multiplexer 166 selects one of the waveform signals FIRE1-6, i.e., six print waveform signals, based on the selecting signal SELn-0, SELn-1, SELn-2 as outputted from the D flip-flop 164, and outputs the selected waveform signal as a waveform signal Bn.
The drive buffer 168 receives the waveform signal Bn outputted from the multiplexer 166, and supplies it as a drive signal OUTn with the predetermined voltage, to the piezoelectric element corresponding to the nozzle, so as to drive the piezoelectric element.
Further, the driver IC 160 comprises a temperature sensor 170 for measuring the temperature of the ink jet head and transmitting a temperature signal VTEMP of analog voltage to the circuit board in the main body, and a test signal transmitting portion 172 for outputting a test signal CHECK used for testing the driver device before shipping.
As described above, the driver IC is mounted on the ink jet head on the carriage. Therefore, the driver IC is connected to the circuit board in the main body of the ink jet printer, through a flexible printed circuit board (FPC), a flexible flat cable (FFC), or the like, which has a flexibility. Hence, with the increase in the number of the signal lines (FIRE1, FIRE2, FIRE3, FIRE4, FIRE5, FIRE6, SIN0, SIN1, SIN2, VTEMP, CHECK), the width of the cable increases. Accordingly, the conventional arrangement is vulnerable to disconnection of lines when a physical force is applied onto the cable, lowering the reliability. Further, with the increase in the number of nozzles, the pitch of leads of a connector connected to the driver IC, for instance, becomes small, making the structure complex. In addition, increase in the number of core wires of the flexible printed circuit board (FPC) or flexible flat cable (FFC) pushes up the required cost.